Lecture

Wave-Matter Interaction: Diffraction and Diffusion Phenomena

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In course

PHYS-206: Physics IV

Ondes et introduction à la relativité restreinte. ...

Description

This lecture covers the interaction of waves with matter, focusing on diffraction and diffusion phenomena. The instructor begins by reviewing the principles of wave refraction and reflection, emphasizing the coefficients of reflection and transmission. The discussion progresses to the principles of Fermat, which explain how waves behave at interfaces. The lecture then introduces diffraction, particularly Fresnel diffraction, and its significance when the dimensions of obstacles approach the wavelength of the wave. The instructor illustrates these concepts with experiments involving light passing through slits, demonstrating the resulting diffraction patterns. The lecture concludes with an exploration of diffusion, particularly in the context of X-ray interactions with matter, highlighting the historical significance of Röntgen's discovery of X-rays and their applications in understanding material structures. Throughout the lecture, the instructor emphasizes the mathematical relationships governing these phenomena, providing a comprehensive overview of wave behavior in various media.

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Related concepts (32)

Diffraction

Diffraction is the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660.

Fresnel diffraction

In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. It is used to calculate the diffraction pattern created by waves passing through an aperture or around an object, when viewed from relatively close to the object. In contrast the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation. The near field can be specified by the Fresnel number, F, of the optical arrangement.

Fraunhofer diffraction

In optics, the Fraunhofer diffraction equation is used to model the diffraction of waves when plane waves are incident on a diffracting object, and the diffraction pattern is viewed at a sufficiently long distance (a distance satisfying Fraunhofer condition) from the object (in the far-field region), and also when it is viewed at the focal plane of an imaging lens. In contrast, the diffraction pattern created near the diffracting object and (in the near field region) is given by the Fresnel diffraction equation.

Wave

In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (resting) value at some frequency. When the entire waveform moves in one direction, it is said to be a traveling wave; by contrast, a pair of superimposed periodic waves traveling in opposite directions makes a standing wave.

Reflection (physics)

Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection (for example at a mirror) the angle at which the wave is incident on the surface equals the angle at which it is reflected. In acoustics, reflection causes echoes and is used in sonar. In geology, it is important in the study of seismic waves.

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